1. Field of the Invention
The present invention relates to a die for molding boot for constant-velocity universal joint (hereinafter being referred to as “CVJ” boot), CVJ boot which has an irregularity ma king an undercut with respect to the direction of opening the die on the inner peripheral surface. Moreover, it relates to using that die, thereby providing a process for molding CVJ boot.
2. Description of the Related Art
A CVJ boot comprises a minor-diameter cylindrical portion, a major-diameter cylindrical portion, and a bellows portion. The minor-diameter cylindrical portion has a given diameter. The major-diameter cylindrical portion has a diameter that is larger than the diameter of the minor-diameter cylindrical portion, and is disposed to separate away from the minor-diameter cylindrical portion as well as to be coaxial with the minor-diameter cylindrical portion. The bellows portion has a configuration of circular truncated cone substantially, and connects the minor-diameter cylindrical portion with the major-diameter cylindrical portion integrally. Accordingly, when molding the CVJ boot by injection molding, it might be difficult to remove or release a molded article from a die because the resulting bellows portion makes an undercut with respect to the molding face of a core mold for molding the inner peripheral configuration of the bellows portion. Consequently, it has been heretofore common conventionally to mold at least the bellows portion by blow molding. Note that injection blow molding has also been used not only to mold the bellows portion by blow molding but also to mold the major-diameter cylindrical portion and/or the minor-diameter cylindrical portion by injection molding.
However, it might be difficult to mold the inner peripheral surface of the bellows portion with higher accuracy, as well as to control the wall thickness of the bellows portion highly accurately, by blow molding. Accordingly, it has been necessary to examine complicated production technologies, such as stabilizing the wall thickness by controlling the height between the crests and roots in the bellows portion. Moreover, the injection blow molding might have been associated with such problems that not only the facilities might have become large-sized but also the molding cycle might have become prolonged, because it has been needed to carry out two steps, the injection molding step and the blow molding step. Consequently, it has been longed for making it possible to mold the bellows portion as well by injection molding.
Yet, the injection molding might possibly have led to the problem with how to remove or release the bellows portion from the core mold, as described above. Hence, it is possible to think of using such a foldable core for molding as disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 62-56,113, for instance. The foldable core is used for molding a can that is provided with an inwardly-directed lip, for instance. The foldable core comprises a tapered central member, an inner segment, and an outer segment. Moreover, the tapered central member, which moves axially, makes each of the inner segment and outer segment move diametrically. In addition, the outer segment is provided with a groove for molding the inwardly-directed lip. Thus, the groove moves diametrically along with the outer segment in a direction of getting away from the inwardly-directed lip to be molded, thereby inhibiting the resulting inwardly-directed lip from making an undercut.
Japanese Unexamined Patent Publication (KOKAI) Gazette No. 62-56, 113 also discloses a core for molding. In the core being disclosed, three inner segments, and three outer segments are laid out symmetrically around a tapered central member. However, the thus constructed core has such a problem that the inner segments and outer segments are limited in terms of the magnitude in the diametrical movement, respectively, because the inner segments have interfered with each other promptly, or because the outer segments have interfered with each other promptly, after the tapered central member starts retracting. That is, the disclosed core only makes it possible to mold lips having restricted heights alone that do not turn into undercuts, but has not enabled manufacturers to mold a molded article having a constituent part that makes a greater undercut, such as the bellows portion of CVJ boot in which the heights between the crests and roots are larger.